Downscan imaging sonar

ABSTRACT

A downscan imaging sonar utilizes a linear transducer element to provide improved images of the sea floor and other objects in the water column beneath a vessel. A transducer array may include a plurality of transducer elements and each one of the plurality of transducer elements may include a substantially rectangular shape configured to produce a sonar beam having a beamwidth in a direction parallel to longitudinal length of the transducer elements that is significantly less than a beamwidth of the sonar beam in a direction perpendicular to the longitudinal length of the transducer elements. The plurality of transducer elements may be positioned such that longitudinal lengths of at least two of the plurality of transducer elements are parallel to each other. The plurality of transducer elements may also include at least a first linear transducer element, a second linear transducer element and a third linear transducer element.

RELATED APPLICATION

The present application invention is a Continuation of U.S. patentapplication Ser. No. 14/072,519, filed Nov. 5, 2013, entitled “DownscanImaging Sonar,” which is a Continuation of U.S. patent application Ser.No. 13/627,318, filed Sep. 26, 2012, entitled “Downscan Imaging Sonar,”now issued as U.S. Pat. No. 8,605,550, which is a Continuation of U.S.patent application Ser. No. 12/460,139, filed Jul. 14, 2009, entitled“Downscan Imaging Sonar,” now issued as U.S. Pat. No. 8,305,840, each ofwhich are incorporated by reference in their entireties.

FIELD OF THE INVENTION

Embodiments of the present invention relate generally to sonar systems,and more particularly, to providing a downscan imaging sonar using alinear transducer.

BACKGROUND OF THE INVENTION

Sonar has long been used to detect waterborne or underwater objects. Forexample, sonar devices may be used to determine depth and bottomtopography, detect fish or other waterborne contacts, locate wreckage,etc. In this regard, due to the extreme limits to visibility underwater,sonar is typically the most accurate way for individuals to locateobjects underwater. Devices such as transducer elements, or simplytransducers, have been developed to produce sound or vibrations at aparticular frequency that is transmitted into and through the water andalso to detect echo returns from the transmitted sound that return tothe transducer after reflecting off an object. The transducers canconvert electrical energy into sound energy and also convert soundenergy (e.g., via detected pressure changes) into an electrical signal,although some transducers may act only as a hydrophone for convertingsound energy into an electrical signal without having a transmittingcapability. The transducers are often made using piezoelectricmaterials.

A typical transducer produces a beam pattern that emanates as a soundpressure signal from a small source such that the sound energy generatesa pressure wave that expands as it moves away from the source. Forinstance, a circular transducer (e.g., a cylindrical shaped crystal witha circular face) typically creates a conical shaped beam with the apexof the cone being located at the source. Any reflected sound thenreturns to the transducer to form a return signal that may beinterpreted as a surface of an object. Such transducers have often beendirected in various directions from surfaced or submerged vessels inorder to attempt to locate other vessels and/or the seabed for thepurposes of navigation and/or target location.

Since the development of sonar, display technology has also beenimproved in order to enable better interpretation of sonar data. Stripchart recorders and other mechanical output devices have been replacedby, for example, digital displays such as LCDs (liquid crystaldisplays). Current display technologies continue to be improved in orderto provide, for example, high quality sonar data on multi-color, highresolution displays having a more intuitive output than early sonarsystems were capable of producing.

With display capabilities advancing to the point at which richlydetailed information is able to be displayed, attention has turned backto the transducer in order to provide higher quality data for display.Furthermore, additional uses have been developed for sonar systems astransducer and display capabilities have evolved. For example, sonarsystems have been developed to assist fishermen in identifying fishand/or the features that tend to attract fish. Historically, these typesof sonar systems primarily analyzed the column of water beneath awatercraft with a cylindrical piezo element that produces a conicalbeam, known as a conical beam transducer or simply as a circulartransducer referring to the shape of the face of the cylindricalelement. However, with the advent of sidescan sonar technology,fishermen were given the capability to view not only the column of waterbeneath their vessel, but also view water to either side of theirvessel.

Sidescan sonar can be provided in different ways and with differentlevels of resolution. As its name implies, sidescan sonar is directed tolook to the side of a vessel and not below the vessel. In fact, manysidescan sonar systems (e.g., swath and bathymetry sonar systems) havedrawn public attention for their performance in the location of famousshipwrecks and for providing very detailed images of the ocean floor,but such systems are costly and complex. Sidescan sonar typicallygenerates a somewhat planar fan-shaped beam pattern that is relativelynarrow in beamwidth in a direction parallel to the keel of a vesseldeploying the sidescan sonar and is relatively wide in beamwidth in adirection perpendicular to the keel of the vessel. It may be provided insome cases using multibeam sonar systems. Such multibeam sonar systemsare typically comprised of a plurality of relatively narrowly focusedconventional circular transducer elements that are arrayed next to eachother to produce an array of narrowly focused adjacent conical beamsthat together provide a continuous fan shaped beam pattern. FIG. 1 showsan example of a series of conventional (generally circular) transducerelements 10 arrayed in an arc to produce a multibeam sonar system. FIG.2 shows a typical fan shaped beam pattern 12 produced by the multibeamsonar system of FIG. 1 as the beam pattern is projected onto the seabed.

However, multibeam sonar systems typically require very complex systemsto support the plurality of transducers that are employed in order toform the multibeam sonar system. For example, a typical system diagramis shown in FIG. 3, which includes a display 20 driven by a sonar signalprocessor 22. The sonar signal processor 22 processes signals receivedfrom each of a plurality of transducers 26 that are fed to the sonarsignal processor 22 by respective different transceivers 24 that arepaired with each of the transducers 26. Thus, conventional multibeamsonar systems tend to include a large number of transceivers andcorrespondingly introduce complexity in relation to processing the datasuch systems produce.

More recently, ceramic sidescan transducer elements have been developedthat enable the production of a fan shaped sonar beam directed to oneside of a vessel. Accordingly, the sea floor on both sides of the vesselcan be covered with two elements facing on opposite sides of the vessel.These types of sidescan transducer elements are linear, rather thancylindrical, and provide a somewhat planar fan-shaped beam pattern usinga single transducer to provide sidescan sonar images without utilizingthe multibeam array described above. However, employment of these typesof sidescan elements typically leaves the column of water beneath thevessel either un-monitored, or monitored using conical beam or circulartransducers. In this regard, FIG. 4 illustrates an example of aconventional sidescan sonar with linear sidescan transducer elementsoriented to produce fan-shaped beams 27 directed from opposite sides ofthe vessel and a conical beam 28 projecting directly below the vessel.These conical beams have conventionally been provided using conventionalcylindrical transducers to produce depth information since sidescantransducers are typically not as useful for providing depth or watercolumn feature information, such as fish targets. However, cylindricaltransducers provide poor quality images for sonar data relating to thestructure on the bottom or in the water column directly below thevessel.

Accordingly, it may be desirable to develop a sonar system that iscapable of providing an improved downscan imaging sonar.

BRIEF SUMMARY OF THE INVENTION

Accordingly, embodiments of the present invention employ a lineartransducer, directed downward to receive high quality images relative tothe water column and bottom features directly beneath the lineartransducer and the vessel on which the linear transducer is employed.Some other embodiments, in addition to the use of a linear transducerdirected downward, also employ at least one sidescan transducer element(e.g., a linear transducer oriented away from the side of the vessel) toensonify (e.g., emit sonar pulses and detect echo returns) the sea flooron the sides of a vessel. Accordingly, better quality sonar images maybe provided for the water column and bottom features beneath the vessel,of a quality that was unavailable earlier. Moreover, embodiments of thepresent invention may simplify the processing involved in producing highquality sonar images.

In one exemplary embodiment, a transducer array is provided. Thetransducer array may include a housing and a linear transducer element.The housing may be mountable to a watercraft capable of traversing asurface of a body of water. The linear transducer element may bepositioned within the housing and may have a substantially rectangularshape configured to produce a sonar beam having a beamwidth in adirection parallel to longitudinal length of the linear transducerelement that is significantly less than a beamwidth of the sonar beam ina direction perpendicular to the longitudinal length of the transducerelement. The linear transducer element may also be positioned within thehousing to project sonar pulses in a direction substantiallyperpendicular to a plane corresponding to the surface.

In another exemplary embodiment, a transducer array is provided. Thetransducer array may include a plurality of transducer elements and eachone of the plurality of transducer elements may include a substantiallyrectangular shape configured to produce a sonar beam having a beamwidthin a direction parallel to longitudinal length of the transducerelements that is significantly less than a beamwidth of the sonar beamin a direction perpendicular to the longitudinal length of thetransducer elements. The plurality of transducer elements may bepositioned such that longitudinal lengths of at least two of theplurality of transducer elements are parallel to each other. Theplurality of transducer elements may also include at least a firstlinear transducer element, a second linear transducer element and athird linear transducer element. The first linear transducer element maybe positioned within the housing to project sonar pulses from a firstside of the housing in a direction generally perpendicular to acenterline of the housing. The second linear transducer element may bepositioned within the housing to lie in a plane with the first lineartransducer element and project sonar pulses from a second side of thehousing that is generally opposite of the first side. The third lineartransducer element may be positioned within the housing to project sonarpulses in a direction generally perpendicular to the plane.

In another exemplary embodiment, a sonar system is provided. The sonarsystem may include a transducer array and a sonar module. The transducerarray may include a plurality of transducer elements and each one of theplurality of transducer elements may include a substantially rectangularshape configured to produce a sonar beam having a beamwidth in adirection parallel to longitudinal length of the transducer elementsthat is significantly less than a beamwidth of the sonar beam in adirection perpendicular to the longitudinal length of the transducerelements. The plurality of transducer elements may be positioned suchthat longitudinal lengths of at least two of the plurality of transducerelements are parallel to each other. The plurality of transducerelements may also include at least a first linear transducer element, asecond linear transducer element and a third linear transducer element.The first linear transducer element may be positioned within the housingto project sonar pulses from a first side of the housing in a directiongenerally perpendicular to a centerline of the housing. The secondlinear transducer element may be positioned within the housing to lie ina plane with the first linear transducer element and project sonarpulses from a second side of the housing that is generally opposite ofthe first side. The third linear transducer element may be positionedwithin the housing to project sonar pulses in a direction generallyperpendicular to the plane. The sonar module may be configured to enableoperable communication with the transducer array. The sonar module mayinclude a sonar signal processor configured to process sonar returnsignals received via the transducer array, and a transceiver configuredto provide communication between the transducer array and the sonarsignal processor.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the U.S. Patent and TrademarkOffice upon request and payment of the necessary fee.

Having thus described the invention in general terms, reference will nowbe made to the accompanying drawings, which are not necessarily drawn toscale, and wherein:

FIG. 1 is a diagram illustrating an example of a series of conventionaltransducer elements 10 arrayed to produce a multibeam sonar system;

FIG. 2 illustrates a fan shaped beam pattern produced by theconventional multibeam sonar system of FIG. 1 as the beam pattern isprojected onto the seabed;

FIG. 3 is a block diagram of a conventional multibeam sonar system forthe system shown in FIG. 1;

FIG. 4 is a diagram illustrating a conventional sidescan sonar system;

FIG. 5 is a basic block diagram illustrating a sonar system according toan exemplary embodiment of the present invention;

FIG. 6 is a diagram illustrating a more detailed view of a transducerarray according to an exemplary embodiment of the present invention;

FIG. 7A illustrates a side view showing a beam pattern produced by thetransducer array according to an exemplary embodiment of the presentinvention;

FIG. 7B illustrates a top view showing a beam pattern produced by thetransducer array according to an exemplary embodiment of the presentinvention;

FIG. 8A is a diagram illustrating a cross section of components in acontainment volume of a housing according to an exemplary embodiment ofthe present invention;

FIG. 8B is a diagram illustrating a cross section of components in acontainment volume of a housing according to another exemplaryembodiment of the present invention;

FIG. 9A shows an example of beam coverage for an 800 kHz operatingfrequency in one exemplary embodiment of the present invention;

FIG. 9B shows an example of beam coverage for a 455 kHz operatingfrequency in one exemplary embodiment of the present invention;

FIG. 10A illustrates a projection, onto a substantially flat sea bed, ofthe beam pattern of an exemplary transducer array providing gaps betweenfan shaped beams produced by a transducer array in which transducerelements are positioned to provide coplanar beams with gaps therebetweenaccording to an exemplary embodiment of the present invention;

FIG. 10B illustrates a projection, onto a substantially flat sea bed, ofthe beam pattern of an exemplary transducer array providing gaps betweenthe fan shaped beams produced by a transducer array in which thetransducer elements are positioned to provide gaps with planarseparation therebetween according to another exemplary embodiment of thepresent invention;

FIG. 11A shows an example of a view of the beam coverage associated withthe exemplary embodiment of FIG. 9A in which the beam coverage isextended to the bottom of a flat bottomed body of water according to anexemplary embodiment of the present invention;

FIG. 11B illustrates example sidescan images that may be produced basedon data from sidescan beams shown in FIG. 11A according to an exemplaryembodiment of the present invention;

FIG. 11C illustrates example linear downscan images that may be producedbased on data from linear downscan beams shown in FIG. 11A according toan exemplary embodiment of the present invention;

FIG. 12A illustrates example sidescan images that may be produced basedon data from sidescan beams;

FIG. 12B illustrates a side-by-side comparison of images produced by adownscan linear transducer element according to an exemplary embodimentand a corresponding conical downscan image;

FIG. 12C illustrates another side-by-side comparison of images producedby a downscan linear transducer element according to an exemplaryembodiment and a corresponding conical downscan image;

FIG. 12D illustrates still another side-by-side comparison of imagesproduced by a downscan linear transducer element according to anexemplary embodiment and a corresponding conical downscan image;

FIG. 12E illustrates yet another side-by-side comparison of imagesproduced by a downscan linear transducer element according to anexemplary embodiment and a corresponding conical downscan image;

FIG. 12F illustrates yet still another side-by-side comparison of imagesproduced by a downscan linear transducer element according to anexemplary embodiment and a corresponding conical downscan image;

FIG. 13A is a diagram illustrating an example of a sea bottom structureviewed through a linear downscan transducer element according to anexemplary embodiment;

FIG. 13B is a diagram illustrating an example of a fan shaped beam froma linear downscan transducer compared to a conical beam from acylindrical transducer for the sea bottom structure illustrated in FIG.13A according to an exemplary embodiment;

FIG. 14 is a basic block diagram illustrating a sonar system accordingto an exemplary embodiment of the present invention;

FIG. 15A illustrates an example of a top view of the beam overlap thatmay occur in situations where a linear downscan transducer and acircular downscan transducer are employed according to an exemplaryembodiment of the present invention;

FIG. 15B shows side views of the same beam overlap shown in FIG. 15Afrom the starboard side of a vessel and from ahead of the bow of thevessel according to an exemplary embodiment of the present invention;

FIG. 16A is a diagram showing a perspective view of a linear downscantransducer and a circular downscan transducer within a single housingfrom a point above the housing according to an exemplary embodiment ofthe present invention;

FIG. 16B is a perspective view from one side of the housing of FIG. 16Aat a point substantially perpendicular to a longitudinal axis of thehousing according to an exemplary embodiment of the present invention;

FIG. 16C is a perspective view from the front side of the housing ofFIG. 16A at a point looking straight down the longitudinal axis of thehousing according to an exemplary embodiment of the present invention;

FIG. 17A is a diagram showing a perspective view of a linear downscantransducer within a single housing from a point above the housingaccording to an exemplary embodiment of the present invention;

FIG. 17B is a perspective view from one side of the housing of FIG. 17Aat a point substantially perpendicular to a longitudinal axis of thehousing according to an exemplary embodiment of the present invention;and

FIG. 17C is a perspective view from the front side of the housing ofFIG. 17A at a point looking straight down the longitudinal axis of thehousing according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary embodiments of the present invention now will be describedmore fully hereinafter with reference to the accompanying drawings, inwhich some, but not all embodiments of the invention are shown. Indeed,the invention may be embodied in many different forms and should not beconstrued as limited to the exemplary embodiments set forth herein;rather, these embodiments are provided so that this disclosure willsatisfy applicable legal requirements. Like reference numerals refer tolike elements throughout.

FIG. 5 is a basic block diagram illustrating a sonar system 30 for usewith multiple exemplary embodiments of the present invention. As shown,the sonar system 30 may include a number of different modules orcomponents, each of which may comprise any device or means embodied ineither hardware, software, or a combination of hardware and softwareconfigured to perform one or more corresponding functions. For example,the sonar system 30 may include a sonar signal processor 32, atransceiver 34 and a transducer array 36 and/or numerous otherperipheral devices such as one or more displays 38. One or more of themodules may be configured to communicate with one or more of the othermodules to process and/or display data, information or the like from oneor more of the modules. The modules may also be configured tocommunicate with one another in any of a number of different mannersincluding, for example, via a network 40. In this regard, the network 40may be any of a number of different communication backbones orframeworks including, for example, Ethernet, the NMEA 2000 framework orother suitable networks.

The display 38 may be configured to display images and may include orotherwise be in communication with a user interface 39 configured toreceive an input from a user. The display 38 may be, for example, aconventional LCD (liquid crystal display), a touch screen display, orany other suitable display known in the art upon which images may berendered. Although each display 38 of FIG. 5 is shown as being connectedto the sonar signal processor 32 via the network and/or via an Ethernethub, the display 38 could alternatively be in direct communication withthe sonar signal processor 32 in some embodiments, or the display 38,sonar signal processor 32 and user interface 39 could be in a singlehousing. The user interface 39 may include, for example, a keyboard,keypad, function keys, mouse, scrolling device, input/output ports,touch screen, or any other mechanism by which a user may interface withthe system. Moreover, in some cases, the user interface 39 may be aportion of one or more of the displays 38.

The transducer array 36 according to an exemplary embodiment may beprovided in one or more housings that provide for flexible mounting withrespect to a hull of the vessel on which the sonar system 30 isemployed. In this regard, for example, the housing may be mounted ontothe hull of the vessel or onto a device or component that may beattached to the hull (e.g., a trolling motor or other steerable device,or another component that is mountable relative to the hull of thevessel), including a bracket that is adjustable on multiple axes,permitting omnidirectional movement of the housing. The transducer array36 may include one or more transducer elements positioned within thehousing, as described in greater detail below, and each of thetransducer elements may be configured to be directed to cover adifferent area such that one transducer element covers one side of thevessel with a fan shaped beam, another transducer element covers theopposite side of the vessel with a fan shaped beam, and the third fanshaped beam covers a region between the other transducer elementsdirected below the vessel. In an exemplary embodiment, each of thetransducer elements of the transducer array 36 may be substantiallyidentical in terms of construction and therefore may be different onlyby virtue of the orientation of the respective transducer elements. Thetransducer array 36 may be configured to both transmit and receive soundpressure waves. However, in some cases, the transducer array 36 couldinclude separate elements for transmission and reception. The transducerarray 36 is described in greater detail below in reference to FIG. 6.

In an exemplary embodiment, the sonar signal. processor 32, thetransceiver 34 and an Ethernet hub 42 or other network hub may form asonar module 44. As such, for example, in some cases, the transducerarray 36 may simply be placed into communication with the sonar module44, which may itself be a mobile device that may be placed (but notnecessarily mounted in a fixed arrangement) in the vessel to permit easyinstallation of one or more displays 38, each of which may be remotelylocated from each other and operable independent of each other. In thisregard, for example, the Ethernet hub 42 may include one or morecorresponding interface ports for placing the network 40 incommunication with each display 38 in a plug-n-play manner. As such, forexample, the Ethernet hub 42 may not only include the hardware needed toenable the displays 38 to be plugged into communication with the network40 via the Ethernet hub 42, but the Ethernet hub 42 may also include orotherwise be in communication with software modules for providinginformation to enable the sonar module 44 to communicate with one ormore different instances of the display 38 that may or may not be thesame model or type of display and that may display the same or differentinformation. In other words, the sonar module 44 may store configurationsettings defining a predefined set of display types with which the sonarmodule is compatible so that if any of the predefined set of displaytypes are placed into communication with the sonar module 44, the sonarmodule 44 may operate in a plug-n-play manner with the correspondingdisplay types. Accordingly, the sonar module 44 may include a memorystoring device drivers accessible to the Ethernet hub 42 to enable theEthernet hub 42 to properly work with displays for which the sonarmodule 44 is compatible. The sonar module 44 may also be enabled to beupgraded with additional device drivers to enable expansion of thenumbers and types of devices with which the sonar module 44 may becompatible. In some cases, the user may select a display type to checkwhether a the display type is supported and, if the display type is notsupported, contact a network entity to request software and/or driversfor enabling support of the corresponding display type.

The sonar signal processor 32 may be any means such as a device orcircuitry operating in accordance with software or otherwise embodied inhardware or a combination of hardware and software (e.g., a processoroperating under software control or the processor embodied as anapplication specific integrated circuit (ASIC) or field programmablegate array (FPGA) specifically configured to perform the operationsdescribed herein, or a combination thereof) thereby configuring thedevice or circuitry to perform the corresponding functions of the sonarsignal processor 32 as described herein. In this regard, the sonarsignal processor 32 may be configured to analyze electrical signalscommunicated thereto by the transceiver 34 to provide sonar dataindicative of the size, location, shape, etc. of objects detected by thesonar system 30. In some cases, the sonar signal processor 32 mayinclude a processor, a processing element, a coprocessor, a controlleror various other processing means or devices including integratedcircuits such as, for example, an ASIC, FPGA or hardware accelerator,that is configured to execute various programmed operations orinstructions stored in a memory device. The sonar signal processor mayfurther or alternatively embody multiple compatible additional hardwareor hardware and software items to implement signal processing orenhancement features to improve the display characteristics or data orimages, collect or process additional data, such as time, temperature,GPS information, waypoint designations, or others, or may filterextraneous data to better analyze the collected data. It may furtherimplement notices and alarms, such as those determined or adjusted by auser, to reflect depth, presence of fish, proximity of other watercraft,etc. Still further, the processor, in combination with suitable memory,may store incoming transducer data or screen images for future playbackor transfer, or alter images with additional processing to implementzoom or lateral movement, or to correlate data, such as fish or bottomfeatures to a GPS position or temperature. In an exemplary embodiment,the sonar signal processor 32 may execute commercially availablesoftware for controlling the transceiver 34 and/or transducer array 36and for processing data received therefrom. Further capabilities of thesonar signal processor 32 and other aspects related to the sonar moduleare described in U.S. patent application Ser. No. 12/460,093, entitled“Linear and Circular Downscan Imaging Sonar” filed on even dateherewith, the disclosure of which is incorporated herein by reference inits entirety.

The transceiver 34 may be any means such as a device or circuitryoperating in accordance with software or otherwise embodied in hardwareor a combination of hardware and software (e.g., a processor operatingunder software control or the processor embodied as an ASIC or FPGAspecifically configured to perform the operations described herein, or acombination thereof) thereby configuring the device or circuitry toperform the corresponding functions of the transceiver 34 as describedherein. In this regard, for example, the transceiver 34 may includecircuitry for providing transmission electrical signals to thetransducer array 36 for conversion to sound pressure signals based onthe provided electrical signals to be transmitted as a sonar pulse. Thetransceiver 34 may also include circuitry for receiving electricalsignals produced by the transducer array 36 responsive to sound pressuresignals received at the transducer array 36 based on echo or otherreturn signals received in response to the transmission of a sonarpulse. The transceiver 34 may be in communication with the sonar signalprocessor 32 to both receive instructions regarding the transmission ofsonar signals and to provide information on sonar returns to the sonarsignal processor 32 for analysis and ultimately for driving one or moreof the displays 38 based on the sonar returns.

FIG. 6 is a diagram illustrating a more detailed view of the transducerarray 36 according to an exemplary embodiment. As shown in FIG. 6, thetransducer array 36 may include a housing 50 that may include mountingholes 52 through which screws, rivets, bolts or other mounting devicesmay be passed in order to fix the housing 50 to a mounting bracket, adevice attached to a vessel or to the hull of the vessel itself.However, in some cases, the housing 50 may be affixed by welding,adhesive, snap fit or other coupling means. The housing 50 may bemounted to a portion of the vessel, or to a device attached to thevessel, that provides a relatively unobstructed view of both sides ofthe vessel. Thus, for example, the housing 50 may be mounted on or nearthe keel (or centerline) of the vessel, on a fixed or adjustablemounting bracket that extends below a depth of the keel (or centerline)of the vessel, or on a mounting device that is offset from the bow orstem of the vessel. The housing 50 may include a recessed portiondefining containment volume 54 for holding transducer elements 60. Therecessed portion defining the containment volume may extend away fromthe hull of the vessel on which the housing 50 is mounted and thereforeprotrude into the water on which the vessel operates (or in which thevessel operates in a case where the transducer array 36 is mounted to atow fish). To prevent cavitation or the production of bubbles due touneven flow over the housing 50, the housing 50 (and in particular thecontainment volume portion of the housing) may have a gradual, roundedor otherwise streamlined profile to permit laminar flow of water overthe housing 50. In some examples, an insulated cable 58 may provide aconduit for wiring to communicatively couple the transducer elements 60to the sonar module 44.

Each of the transducer elements 60 may be a linear transducer element.Thus, for example, each of the transducer elements 60 may besubstantially rectangular in shape and made from a piezoelectricmaterial such as a piezoelectric ceramic material, as is well known inthe art and may include appropriate shielding (not shown) as is wellknown in the art. The piezoelectric material being disposed in arectangular arrangement provides for an approximation of a linear arrayhaving beamwidth characteristics that are a function of the length andwidth of the rectangular face of the transducer elements and thefrequency of operation. In an exemplary embodiment, the transducerelements 60 may be configured to operate in accordance with at least twooperating frequencies. In this regard, for example, a frequencyselection capability may be provided by the sonar module 44 to enablethe user to select one of at least two frequencies of operation. In oneexample, one operating frequency may be set to about 800 kHz and anotheroperating frequency may be set to about 455 kHz. Furthermore, the lengthof the transducer elements may be set to about 120 mm while the width isset to about 3 mm to thereby produce beam characteristics correspondingto a bearing fan of about 0.8 degrees by about 32 degrees at 800 kHz orabout 1.4 degrees by about 56 degrees at 455 kHz. However, in general,the length and width of the transducer elements 60 may be set such thatthe beamwidth of sonar beam produced by the transducer elements 60 in adirection parallel to a longitudinal length (L) of the transducerelements 60 is less than about five percent as large as the beamwidth ofthe sonar beam in a direction (w) perpendicular to the longitudinallength of the transducer elements 60. (See generally FIGS. 7A, 7B, 9A,9B.) It should be noted that although the widths of various beams areshown and described herein, the widths being referred to do notnecessarily correspond to actual edges defining limits to where energyis placed in the water. As such, although beam patterns and projectionsof beam patterns are generally shown herein as having fixed andtypically geometrically shaped boundaries, those boundaries merelycorrespond to the −3 dB (or half power) points for the transmittedbeams. In other words, energy measured outside of the boundaries shownis less than half of the energy transmitted. Thus, the boundaries shownare merely theoretical half power point boundaries.

Although dual frequency operations providing a specific beam fan foreach respective element for given lengths are described above, it shouldbe understood that other operating ranges could alternatively beprovided with corresponding different transducer element sizes andcorresponding different beamwidth characteristics. Moreover, in somecases, the sonar module 44 may include a variable frequency selector, toenable an operator to select a particular frequency of choice for thecurrent operating conditions. However, in all cases where thelongitudinal length of the transducer elements 60 is generally alignedwith the centerline of the vessel, the rectangular shape of thetransducer elements 60 provides for a narrow beamwidth in a directionsubstantially parallel to the centerline of the vessel and widebeamwidth in a direction substantially perpendicular to the centerlineof the vessel. However, if the transducer array 36 is mounted in adifferent fashion or to a rotatable accessory on the vessel (e.g., atrolling motor mount), the fan-shaped beams produced will have the widebeamwidth in a direction substantially perpendicular to the longitudinallength of the transducer elements 60 and a narrow beamwidth in adirection substantially parallel to the longitudinal length of thetransducer elements 60. Thus, the sonar could also be oriented toprovide fore and aft oriented fan-shaped beams or any other orientationrelative to the vessel in instances where motion of the vessel is notnecessarily in a direction aligned with the centerline of the vessel.

FIGS. 7A and 7B show side and top views, respectively, illustrating thebeam characteristics produced by an exemplary embodiment of the presentinvention. In this regard, FIG. 7A illustrates a side view showing thetransducer array 36 mounted to a bracket that extends from the aft endof the centerline of the vessel (e.g., boat). As shown in FIG. 7A, thebeam produced by the transducer array 36 is relatively narrow in thedirection substantially parallel to the centerline of the vessel if thetransducer elements are aligned for a generally coplanar beam. FIG. 7Aalso includes a cutaway view of the transducer array 36 to show theorientation of the transducer elements 60 in context relative to thevessel according to this example. Meanwhile, FIG. 7B shows a top view ofthe beam produced by the transducer assembly 36 if the transducerelements are aligned for a generally coplanar beam. As shown in FIG. 7B,the beam produced by the transducer array is relatively wide in thedirection substantially perpendicular to the centerline of the vesselthereby producing a fan-shaped beam pattern extending out to both sidesand also covering the water column beneath the vessel, as describedbelow. FIG. 7B also includes a cutaway view of the transducer array 36to show the orientation of the transducer elements 60 in contextrelative to the vessel according to this example.

FIG. 8A is a diagram illustrating a cross section of components in thecontainment volume 54 according to an exemplary embodiment. Inparticular, FIG. 8A illustrates the arrangement of the linear transducerelements 60 within the containment volume 54. The transducer elements60, which may include a port side element 62 positioned to scansubstantially to the port side of the vessel, a starboard side element64 positioned to scan substantially to the starboard side of the vessel,and a downscan element 66 positioned to scan substantially below thevessel. As shown in FIG. 8A, in an exemplary embodiment, both the portside element 62 and the starboard side element 64 may be oriented toface slightly below a surface of the water on which the vessel travels.In one example, both the port side element 62 and the starboard sideelement 64 may be oriented such that the widest dimension of thebeamwidth of each respective element is centered at 30 degrees below aplane substantially parallel to the surface of the water. Meanwhile, thedownscan linear element 66 may be positioned such that the widestdimension of the beamwidth of the downscan element 66 is centered at 90degrees below the plane substantially parallel to the surface of thewater. In other words, the downscan element 66 has the central portionof its fan shape aimed straight down. The containment volume 54 mayinclude electrical connections (not shown) to communicate with thetransceiver 34 and supports, struts, rods or other supporting structuresto secure each of the linear transducer elements 60 in their respectiveorientations. The transducer elements 60 may be held in place orotherwise affixed to the supporting structures via adhesive or any othersuitable joining material and the angles at which the transducerelements 60 are affixed relative to each other and to the housing 50 mayvary as necessary or as desired.

FIG. 8B is a diagram illustrating a cross section of components in thecontainment volume 54 according to an alternative exemplary embodiment.In this regard, FIG. 8B illustrates the arrangement of one lineartransducer element 60 within the containment volume 54. The transducerelement 60 according to this exemplary embodiment is a single lineartransducer (e.g., downscan element 66) positioned to scan substantiallybelow the vessel. As shown in FIG. 8B, the downscan element 66 may bepositioned such that the widest dimension of the beamwidth of thedownscan element 66 is centered at 90 degrees below the planesubstantially parallel to the surface of the water. In other words, thedownscan element 66 has the central portion of its fan shape aimedsubstantially straight down. As discussed above, the containment volume54 may include electrical connections (not shown) to communicate withthe transceiver 34 and supports, struts, rods or other supportingstructures to secure the downscan element 66 in its respectiveorientation. The linear downscan element 66 may be held in place orotherwise affixed to the supporting structures via adhesive or any othersuitable joining material such that transmissions produced by thedownscan element 66 exit the housing 50 substantially at a 90 degreeangle with respect to the plane of the face of the downscan element 66from which the transmissions emanate.

FIG. 9A shows an example of beam coverage for an 800 kHz operatingfrequency in one exemplary embodiment. As such, the beamwidth (e.g.,width between the half power points) of each of the three lineartransducer elements 60 is about 32 degrees. FIG. 9B shows an example ofbeam coverage for a 455 kHz operating frequency in one exemplaryembodiment, thereby providing about 56 degrees of beamwidth for each ofthe three linear transducer elements 60. Accordingly, in each of theexemplary embodiments of FIGS. 9A and 9B, the three fan-shaped segmentstogether produce a discontinuous fan shaped beam. The discontinuity maybe minimized in some instances by selection of transducer elementdimensions and operating frequencies selected to minimize the size ofthe gaps (e.g., zones with sonar beam coverage outside of beam coveragearea as defined by the half power points of the beams) between the beamsof the transducer elements. Alternatively, the physical orientation ofthe transducer elements 60 with respect to each other could be changedin order to minimize the size of the gaps. However, it should be notedthat in most cases some gap should be maintained in order to preventinterference between the beam patterns emanating from the lineartransducer elements 60. Although the fan-shaped segments of an exemplaryembodiment may all lie in the same plane, it may be desirable to alterthe orientation of one or more of the transducer elements 60 such that acorresponding one or more of the fan-shaped segments is outside of theplane of the other fan-shaped segments. The gap could therefore beprovided via planar separation of the fan-shaped segments rather than byproviding separation between the segments within the same plane.

In this regard, FIG. 10A illustrates a projection, onto a substantiallyflat sea bed, of the beam pattern of an exemplary transducer arrayproviding gaps between the boundaries of the projections as defined bythe half power points defining fan shaped beams produced by a transducerarray in which the transducer elements 60 are positioned to providecoplanar beams with gaps therebetween according to an exemplaryembodiment. As such, a first transducer element beam projection 100, asecond transducer element beam projection 102 and a third transducerelement beam projection 104 are all shown lying in the same plane inFIG. 10A. Meanwhile, FIG. 10B illustrates a projection, onto asubstantially flat sea bed, of the beam pattern of an exemplarytransducer array providing gaps between the fan shaped beams produced bya transducer array in which the transducer elements 60 are positioned toprovide gaps with planar separation therebetween according to anotherexemplary embodiment. Thus, the first transducer element beam projection100′, the second transducer element beam projection 102′ and the thirdtransducer element beam projection 104′ are shown lying in differentplanes in FIG. 10B. Notably, in each of FIGS. 10A and 10B, the view isshown from the top looking down onto the sea bed and the beamprojections are not necessarily to scale.

FIG. 11A shows an example of a view of the beam coverage associated withthe embodiment of the example shown in FIG. 9A in which the beamcoverage is extended to the bottom of a flat bottomed body of water. Theillustration of FIG. 11A shows a view looking at the stern of a vessel70 as the vessel 70 is driving away from the viewer (e.g., into thepage). According to this example, a port sidescan beam 72 (e.g., thatmay be produced by port sidescan element 62) extends out to the portside of the vessel 70 providing coverage of the bottom from point A topoint B. Meanwhile, a starboard sidescan beam 74 (e.g., that may beproduced by starboard sidescan element 64) extends out to the starboardside of the vessel 70 from point C to point D. Additionally, a downscanbeam 76 (e.g., that may be produced by downscan element 66) extendsdirectly below the vessel 70 from point E to point F. As shown in FIG.11A, the coverage areas defined between points A and B and points C andD are substantially larger than the coverage area defined between pointsE and F. Based on the increased bottom coverage, the display providedresponsive to data received in the sidescan beams 72 and 74 will bedifferent than the display provided responsive to data received in thedownscan beam 76. FIGS. 11B and 11C show examples of images that maycorrespond to the beam coverage areas shown in FIG. 11A. In this regard,for example, FIG. 11B illustrates possible images that could correspondto the region defined between points A and B and points C and D (e.g.,sidescan images), while FIG. 11C illustrates a possible image that maycorrelate to the coverage area between points E and F (e.g., a lineardownscan image).

FIGS. 12A through 12F show examples of images that may be produced byembodiments of the present invention to illustrate differences betweenthe display produced by a linear downscan element of an embodiment ofthe present invention and either a sidescan or a conventional circulardownscan transducer element. In this regard, FIG. 12A illustrates anexample image that may be produced based on data from the sidescan beams72 and 74. For this example, assume the top of the display (identifiedby arrow 80) shows the most recent data (e.g., corresponding to thevessel's current position) and the bottom of the display (identified byarrow 82) shows the oldest data. Additionally, the right side of thedisplay 84 may correspond to the starboard sidescan beam 74 while theleft side of the display 86 corresponds to the port sidescan beam 72.Brighter pixels illustrated in FIG. 12A correspond to return datareceived in the corresponding sidescan beams. In this regard, dataclosest to dashed line 88 corresponds to the data gathered near point B(for the left side of the display 86) and near point D (for the rightside of the display 84) and data at the left edge of the displaycorresponds to data gathered near point A while data at the right edgeof the display corresponds to data gathered near point C over the timeperiod from the position of arrow 82 to the position of arrow 80. Thus,well over 50% of the display of FIG. 12A (and in many cases 100%) isutilized to show data corresponding to bottom features, e.g. thetopography of and structures attached to the bottom, that have providedreturn data from the sidescan beams 72 and 74. By comparison only asmall portion (e.g., less than 20%) of the display shows any watercolumn features, e.g., data from the water column between the vessel 70and the portions of the bottom covered by each respective sidescan beam.The sidescan beams 72 and 74 also fail to provide depth data. Stillfurther, the sidescan beams fail to provide depth data or bottom featuredata or water column data for that portion of the bottom beneath thevessel, e.g., that portion between reference points B and D and thevessel 70 in FIG. 11.

FIGS. 12B through 12F show on the right side (e.g., right display 90) ofeach figure, exemplary screen shots of a conventional circular downscantransducer image that corresponds to the display (e.g., the left side ofeach figure (left display 92)) produced by the linear downscan elementof an embodiment of the present invention (e.g., downscan element 66).In this regard, the left display of FIG. 12B shows a boulder on theleft, two tree trunks rising up from the bottom near the center of thedisplay, and, possibly, several fish (white spots) near the lower right.The corresponding same features can be vaguely determined from the rightdisplay 90 (i.e., the circular downscan display), but the images aremuch less clear. Similarly, FIGS. 12C, 12D and 12E clearly show verydetailed images of trees rising vertically from the bottom in the leftdisplay 92, while such features are very difficult to distinguish on theright display 90. FIG. 12F clearly shows a downed tree and at least twovertical trees nearby in the left display 92, whereas the same featuresare difficult to discern in the right display 90.

The exemplary linear downscan image on the left side of FIG. 12Bincludes a numerical depth scale 0-40 on the right side, with sonarreflection data being represented on the display screen at thetime-dependent depth using known sonar imaging practices. Boat positionis represented by the numeral 0, or some other desirable icon, for themost recent sonar pings, and the oldest sonar pings are presented by theleft side of the screen, presenting a scrolling image as the boat (andtransducer) move across the water surface over time. The far rightcolumn reflects the intensity of the return echo received at thecircular downscan transducer, plotted adjacent the 0-40 depth scale.

Accordingly, by placing a linear transducer in a downward orientedposition, a much improved image quality is achieved for bottom data andstructures attached to it or rising above it relative to theconventional circular downscan sonar. In this regard, while sidescanimages are valued for their ability to provide detailed images oflaterally distant bottom features, they are unable to provide depth dataor bottom data or water column data below the vessel. A linear downscanelement provides the unexpected advantage of providing detailed imagesof the water column below the vessel (e.g., upwardly extending submergedtrees, fish, etc.), as well as details of the features of the bottom orstructures resting on or rising above the bottom (e.g., rocks, crevices,submerged trees, sunken objects, etc.), and a depth indication that canbe registered (e.g., feet or meters). For example, again referring tothe left image of FIG. 12B, the mass of bright pixels at about 30 feet(as indicated by the numbers in increments of five feet that extend downthe right edge of the left display 92) represent bottom feature data andare indicative of the depth at which the bottom is encountered. Thebottom feature data may also, in some cases, indicate the type of bottom(e.g., rocky, muddy, hard, soft, flat, sloped, smooth, rough, etc.).Thus, sonar returns associated with the bottom in a linear downscandisplay are not only indicative of bottom features, but are alsoindicative of depth and water column data. However, the bottom featuredata represents a relatively small percentage of the overall displayarea. Due to the relatively small percentage of display area that isdevoted to bottom feature data, a relatively large percentage of thedisplay area may be devoted to other data, e.g., data representing thewater column above the bottom). Thus, for example, as shown in FIG. 12B,water column features are represented by data including a boulder andtrees extending from the bottom along with any suspended objects (e.g.,schools of bait fish, individual large fish, etc.), thermoclines, andother features may be displayed in greater detail along with theindication of bottom depth. Meanwhile, even in situations where the zoomlevel of the display is not set such that the lake or sea bottom is nearthe lowest portion of the display (such as in FIG. 12C), the bottomfeatures only account for a small percentage of the display area, whilethe water column features account for more than 50% and the area belowthe lake or sea bottom is essentially featureless.

FIGS. 12B through 12F each show far less than 50% (and typically lessthan 20%) of the display being utilized to show data corresponding tobottom features, and do so for the water column beneath the vessel. Asshown, a linear transducer positioned as a downscan element (e.g.,downscan element 66) according to an exemplary embodiment, is capable ofproviding far more information regarding the water column itself ratherthan merely the bottom features or depth. Thus, water column data can bereceived and displayed, representing schools of fish, individual fishand certain structural features in the water column directly below thevessel 70. Additionally, as shown in FIGS. 12B through 12F, a lineartransducer positioned as a downscan element is also capable of producingdepth data. In this regard, whereas a sidescan image produces relativelyhigh quality images of bottom features (see for example, FIG. 12A), itis unable to produce useful depth data or water column data. A downscanimage produced by a linear transducer according to an exemplaryembodiment of the present invention produces depth data along withbottom feature data and water column data.

FIG. 13A provides an example of a display of the bottom structure asviewed through use of a linear downscan sonar element (e.g., downscanelement 66) of an exemplary embodiment of the present invention. FIG.13B shows the vessel 70 and various bottom features viewed from above.The bottom features include a boulder 120, a vertical tree 122, a rockpile 124, a school of fish 126 and a fallen, horizontal tree 128. FIG.13B also shows a linear transducer downscan fan-shaped sonar beam 130projected onto the bottom as compared to a circular transducer downscanconical beam 132 projected onto the bottom. As can be appreciated fromthe corresponding example display provided in FIG. 13A, since the lineardownscan beam 130 has a narrow aspect in one direction and a broadaspect in the other, the amount of data received and therefore processedfor display is less with respect to each feature for which a return isreceived than for the conical beam 132. There is typically no overlap incoverage from each outgoing sound wave to the next (ping to ping) in thelinear downscan beam 130 whereas there will be such overlap in theconical beam 132. Thus, while data corresponding to the conical beam 132is processed, it produces blurred images due to the additional returndata received. The linear downscan beam 130 is able to produce “cleaner”images that more accurately illustrate feature data that reflects whatobjects are in the water column and on the bottom beneath the vessel.Note, however, that there can be at least partial overlap in the bottomtopography that is sonified by the linear and circular transducer, asshown in FIG. 13B.

By providing the downscan element 66 as a linear transducer element ofthe same type and construction as one or both of the port side linearelement 62 and the starboard side linear element 64, embodiments of thepresent invention provide vivid images of the column of water over whichthe vessel passes in addition to providing vivid images of the watercolumn on both sides of the vessel, which is provided by conventionalsidescan sonar systems that either neglect the column of water beneaththe vessel or only scan such region with a conical beam from atransducer element having a cylindrical shape that is not capable ofproviding the level of detail provided by embodiments of the presentinvention. Moreover, embodiments of the present invention provide highquality images of the column of water over which the vessel passeswithout the high degree of complexity and cost associated with amultibeam system.

FIG. 14 illustrates an exemplary sonar system incorporating linear andcircular downscan transducers 140, 142. The two transducers may be inthe same or separate housings. They typically utilize differentoperational frequencies. Such may also assist in minimizinginterference. Similar to the system illustrated in FIG. 5, thetransducers are operationally connected to the transceivers 144, 146,which configure the transducer outputs for receipt by the sonar signalprocessor 148. The sonar signal processor executes various programsstored or as may be selected by the user interface 150. The Ethernet hub152, network 154, displays 156 and user interface. 150 operate asdescribed for the corresponding components of FIG. 5. The imageprocessor 158 may perform a variety of functions to optimize orcustomize the display images, including such features as split screen toshow multiple different sonar images or data. Examples includeindividual and separate images of GPS, waypoints, mapping, nauticalcharts, GPS tracking, radar, etc., which are typically shownside-by-side or stacked. Additional examples include individual databoxes, such as speed, depth, water, temperature, range or distancescales, location or waypoint, latitude, longitude, time, etc. Stillfurther examples include composite images that combine information fromone or more of these sources, such as the images from the lineardownstream and circular downstream transducers to overlay the images.For example, the traditional “fish arch” image representing a possiblefish using a circular downscan sonar may be imposed over a small whitecircle or oval representing a possible fish using a linear downscansonar. Still further, one image may be colorized to distinguish itvisibly from data representing another image. As such, for example, theimages may be combined using image blending or overlay techniques.Alternatively, individual images may be presented, or different images,simultaneously on different displays without overlay. Image data packetsor streams may also have additional data associated therewith, such astime of day, location, temperature, speed, GPS, etc.

Notably, the example of FIG. 14 may be simplified in some embodiments.In this regard, the radar, map and GPS modules of FIG. 14 along with theEthernet hub 152 may not be included in some embodiments. Moreover, inone example, an embodiment of the present invention may includeessentially only processing circuitry to handle inputs from a linear andcircular transducer array along with a display in a single device. Assuch, for example, all of the electronics for handling linear andcircular transducer inputs may be included along with a display within asingle box, without any Ethernet connection or other peripherals.

FIG. 15A illustrates an example of a top view of the beam overlap thatmay occur in situations where a linear downscan transducer and acircular downscan transducer are employed simultaneously. FIG. 15B showsside views of the same beam overlap shown in FIG. 15A from the starboardside of a vessel (on the left side of the page) and from ahead of thebow of the vessel (on the right side of the page). As shown in FIG. 15A,there is overlap between a conical beam projection 180 showing anexample coverage area of a beam produced by the circular downscantransducer and a downscan beam projection 182 showing an examplecoverage area of a beam produced by the linear downscan transducer. Thedifferences between the beam patterns of the linear and circulardownscan transducers are further illustrated in FIG, 15B in which it canbe seen that the beamwidth 184 of the beam produced by the circulardownscan transducer is substantially the same regardless of the sidefrom which the beam is viewed. However, the beamwidth 186 of the beamproduced by the linear downscan transducer as viewed from the starboardside of the vessel is substantially smaller than the beamwidth 188 ofthe beam produced by the linear downscan transducer as viewed from aheadof the bow of the vessel. Moreover, the beamwidth 188 is wider than thebeamwidth 184, while the beamwidth 186 is narrower than the beamwidth184.

FIGS. 16A through 16C illustrate diagrams of a linear downscantransducer 190 and a circular downscan transducer 192 within a singlestreamlined housing 194 from various different perspectives, In thisregard, FIG. 16A is a perspective view from above the housing 194.Meanwhile, FIG. 16B is a perspective view from one side of the housing194 at a point substantially perpendicular to a longitudinal axis of thehousing 194 and FIG. 16C is a perspective view from the front side ofthe housing 194 at a point looking straight down the longitudinal axisof the housing 194, As shown in FIGS. 16A-16C, the linear downscantransducer 190 and the circular downscan transducer 192 may each bedisposed to be in planes that are substantially parallel with each otherand with a plane in which the longitudinal axis of the housing 194 lies.Generally speaking, the linear downscan transducer 190 and the circulardownscan transducer 192 may also be displosed in line with thelongitudinal axis of the housing 194. Although shown in a particularorder in FIGS. 16A-16C, the ordering of the placement of the lineardownscan transducer 190 and the circular downscan transducer 192 withinthe housing 194 may be reversed in some examples. Furthermore, in somecases, the linear downscan transducer 190 and the circular downscantransducer 192 may each be located in their own respective separatehousings rather than both being within a single housing. FIGS. 16A-16Calso illustrate an example of a mounting device 196 for mounting thehousing 194 to a vessel.

By way of comparison, FIGS. 17A through 17C illustrate diagrams of asingle linear downscan transducer 190 a housing 198 from variousdifferent perspectives. In this regard, FIG. 17A is a perspective viewfrom above the housing 198. Meanwhile, FIG. 17B is a perspective viewfrom one side of the housing 198 at a point substantially perpendicularto a longitudinal axis of the housing 198 and FIG. 17C is a perspectiveview from the front side of the housing 198 at a point looking straightdown the longitudinal axis of the housing 198. As shown in FIGS.17A-17C, by employing only the linear downscan transducer 190 the sizeof the housing 198 may be reduced. In this regard, for example,particularly FIG. 17C shows a reduction in the cross sectional size ofthe housing 198 as compared to the cross sectional size of the housing194 of FIG. 16C. Thus, for example, the housing 198 may introduce lessdrag than the housing 194.

Many modifications and other embodiments of the inventions set forthherein will come to mind to one skilled in the art to which theseembodiments pertain having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it is tobe understood that the inventions are not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

1.-57. (canceled)
 58. A sonar transducer assembly for imaging anunderwater environment beneath a watercraft, the sonar transducerassembly comprising: a housing mountable to the watercraft, wherein thewatercraft defines a center plane that extends from fore to aft of thewatercraft; and a linear downscan transducer element positioned withinthe housing, wherein the linear downscan transducer element isconfigured to produce a fan-shaped sonar beam having a relatively narrowbeamwidth in a direction parallel to a longitudinal length of the lineardownscan transducer element and a relatively wide beamwidth in adirection perpendicular to the longitudinal length of the lineardownscan transducer element, wherein the linear downscan transducerelement is positioned with the longitudinal length thereof extending ina fore-to-aft direction of the housing, wherein the linear downscantransducer element is positioned within the housing to project thefan-shaped sonar beam such that the relatively wide beamwidth spansacross the center plane of the watercraft to cover directly beneath thewatercraft.
 59. The sonar transducer assembly of claim 58, wherein thelinear downscan transducer element is positioned within the housing toproject the fan-shaped sonar beam such that at least a portion of therelatively wide beamwidth spans on each side of the center plane of thewatercraft.
 60. The sonar transducer assembly of claim 58, wherein thefan-shaped sonar beam produced by the linear downscan transducer elementis defined by theoretical boundaries that correspond to half powerpoints for the fan-shaped sonar beam.
 61. The sonar transducer assemblyof claim 60, wherein the half power points are −3 dB.
 62. The sonartransducer assembly of claim 58, wherein the linear downscan transducerelement is positioned within the housing to project the fan-shaped sonarbeam to extend out to both sides of the center plane and cover a watercolumn beneath the watercraft.
 63. The sonar transducer assembly ofclaim 58, wherein the linear downscan transducer element is positionedwithin the housing to project the fan-shaped sonar beam such that awidest portion of the relatively wide beamwidth is centered at thecenter plane.
 64. The sonar transducer assembly of claim 58, furthercomprising a second downscan transducer element positioned within thehousing, the second downscan transducer element being configured toproduce a generally conical beam that is wider than the fan-shaped sonarbeam in a direction parallel to a longitudinal length of the lineardownscan transducer element, wherein the second downscan transducerelement is positioned within the housing to project the conical beam tocover directly beneath the watercraft.
 65. The sonar transducer assemblyof claim 58, further comprising: a first linear sidescan transducerelement positioned within the housing and configured to produce afan-shaped sonar beam, wherein the first linear sidescan transducerelement is positioned within the housing to project the fan-shaped sonarbeam to a first side of the center plane, wherein the first side of thecenter plane corresponds generally to a starboard side of thewatercraft; and a second linear sidescan transducer element positionedwithin the housing and configured to produce a fan-shaped sonar beam,wherein the second linear sidescan transducer element is positionedwithin the housing to project the fan-shaped sonar beam to a second sideof the center plane, wherein the second side of the center planecorresponds generally to a port side of the watercraft.
 66. A sonarsystem comprising: a sonar transducer assembly for imaging an underwaterenvironment beneath a watercraft, the sonar transducer assemblycomprising: a housing mountable to the watercraft, wherein thewatercraft defines a center plane that extends from fore to aft of thewatercraft; and a linear downscan transducer element positioned withinthe housing, wherein the linear downscan transducer element isconfigured to produce a fan-shaped sonar beam having a relatively narrowbeamwidth in a direction parallel to a longitudinal length of the lineardownscan transducer element and a relatively wide beamwidth in adirection perpendicular to the longitudinal length of the lineardownscan transducer element, wherein the linear downscan transducerelement is positioned with the longitudinal length thereof extending ina fore-to-aft direction of the housing, wherein the linear downscantransducer element is positioned within the housing to project thefan-shaped sonar beam such that the relatively wide beamwidth spansacross the center plane of the watercraft to cover directly beneath thewatercraft; a sonar signal processor configured to receive lineardownscan sonar data from the linear downscan transducer element based onsonar returns from the fan-shaped sonar beam produced by the lineardownscan transducer element; and a display configured to present animage corresponding to the linear downscan sonar data.
 67. The sonarsystem of claim 66, wherein the linear downscan transducer element ispositioned within the housing to project the fan-shaped sonar beam suchthat at least a portion of the relatively wide beamwidth spans on eachside of the center plane of the watercraft.
 68. The sonar system ofclaim 66, wherein the fan-shaped sonar beam produced by the lineardownscan transducer element is defined by theoretical boundaries thatcorrespond to half power points for the fan-shaped sonar beam.
 69. Thesonar system of claim 68, wherein the half power points are −3 dB. 70.The sonar system of claim 66, wherein the linear downscan transducerelement is positioned within the housing to project the fan-shaped sonarbeam to extend out to both sides of the center plane and cover a watercolumn beneath the watercraft.
 71. The sonar system of claim 66, whereinthe linear downscan transducer element is positioned within the housingto project the fan-shaped sonar beam such that a widest portion of therelatively wide beamwidth is centered at the center plane.
 72. The sonarsystem of claim 66, wherein the sonar transducer assembly furthercomprises a second downscan transducer element positioned within thehousing, the second downscan transducer element being configured toproduce a generally conical beam that is wider than the fan-shaped sonarbeam in a direction parallel to a longitudinal length of the lineardownscan transducer element, wherein the second downscan transducerelement is positioned within the housing to project the conical beam tocover directly beneath the watercraft, wherein the sonar signalprocessor is configured to receive second downscan sonar data from thesecond downscan transducer element based on sonar returns from theconical sonar beam produced by the second downscan transducer element.73. The sonar system of claim 66, wherein the sonar transducer assemblyfurther comprises: a first linear sidescan transducer element positionedwithin the housing and configured to produce a fan-shaped sonar beam,wherein the first linear sidescan transducer element is positionedwithin the housing to project the fan-shaped sonar beam to a first sideof the center plane, wherein the first side of the center planecorresponds generally to a starboard side of the watercraft; and asecond linear sidescan transducer element positioned within the housingand configured to produce a fan-shaped sonar beam, wherein the secondlinear sidescan transducer element is positioned within the housing toproject the fan-shaped sonar beam to a second side of the center plane,wherein the second side of the center plane corresponds generally to aport side of the watercraft; and wherein the sonar signal processor isconfigured to receive first linear sidescan sonar data from the firstlinear sidescan transducer element based on sonar returns from thefan-shaped sonar beam produced by the first linear sidescan transducerelement, wherein the sonar signal processor is configured to receivesecond linear sidescan sonar data from the second linear sidescantransducer element based on sonar returns from the fan-shaped sonar beamproduced by the second linear sidescan transducer element.
 74. A methodof operating a sonar system, the method comprising: providing a sonartransducer assembly for imaging an underwater environment beneath awatercraft, wherein the sonar transducer assembly comprises: a housingmountable to the watercraft, wherein the watercraft defines a centerplane that extends from fore to aft of the watercraft; and a lineardownscan transducer element positioned within the housing, wherein thelinear downscan transducer element is configured to produce a fan-shapedsonar beam having a relatively narrow beamwidth in a direction parallelto a longitudinal length of the linear downscan transducer element and arelatively wide beamwidth in a direction perpendicular to thelongitudinal length of the linear downscan transducer element, whereinthe linear downscan transducer element is positioned with thelongitudinal length thereof extending in a fore-to-aft direction of thehousing, wherein the linear downscan transducer element is positionedwithin the housing to project the fan-shaped sonar beam such that therelatively wide beamwidth spans across the center plane of thewatercraft to cover directly beneath the watercraft; causing projectionof a fan-shaped sonar beam from the linear downscan transducer element;and receiving sonar returns from the underwater environment based on thefan-shaped sonar beam projected from the linear downscan transducerelement.
 75. The method of claim 74 further comprising: providing asonar signal processor; and receiving, at the sonar signal processor,linear downscan sonar data from the linear downscan transducer elementbased on sonar returns from the fan-shaped sonar beam produced by thelinear downscan transducer element.
 76. The method of claim 75 furthercomprising: providing a display; processing, via the sonar signalprocessor, the linear downscan sonar data to generate an imagecorresponding to the linear downscan sonar data; and causingpresentation of the image on the display.
 77. The method of claim 74,wherein the linear downscan transducer element is positioned within thehousing to project the fan-shaped sonar beam such that at least aportion of the relatively wide beamwidth spans on each side of thecenter plane of the watercraft.